Method of purifying molten iron



Patented Nov. 2'1, 1950 METHOD OF PURIFYING MOLTEN IRON James Fernando Jordan, Huntington Park, Calif.,

assignor to James Jordan Laboratory, Huntington Park, Calif., a partnership No Drawing. Application April 1, 1950, Serial No. 153,500

7 Claims.

My invention relates to the production of ductile nodular cast iron.

This application is a continuation-in-part of my copending application, Serial No. 118,180, filed on Sept. 27, 1949, now abandoned.

The production of ductile nodular graphite cast iron requires the alloying of magnesium with molten cast iron. While there are a number of ways in which this alloying operation may be carried out, extreme difiiculties have been encountered by metallurgists when they attempted to hold the magnesium content of the molten metal within the rather narrow limits required if a ductile product is to be produced. Most of these difficulties arise from the fact that magnesium acts as a refining agent when introduced into molten iron, and that there seems to be no accurate way to predict just how much of the added magnesium will be consumed in such refining the desulphurization and deoxidation of the molten metal, for example. Furthermore, the control laboratory has not been too helpful in informing the metallurgist where the magnesium content of his metal lies, for analytical procedures do not seem to be accurate enough to furnish the required accurate picture of the composition of the metal before it is poured into molds. Wet methods of analysis suiier from the fact that any method of dissolving the cast iron fails to separate the alloyed magnesium from the magnesium present in the metal in the form or" magnesium oxide, magnesium silicate, magnesium nitride, magnesium sulphide, etc.; that is, an acid that will dissolve cast iron will dissolve most compounds of magnesium as well. Spectrographic methods of determining the magnesium content of cast iron are defective in that said methods do not distinguish between magnesium and magnesium compounds.

These dificulties are greatly handicapping the development of the nodular iron industry. The principal object of my invention concerns a solution to these diiiiculties. Other objects will become apparent in the specification and claims.

Present methods of adding the magnesium to the iron usually consist of either estimating or determining the sulphur content of the molten iron, and then adding enough magnesium to the molten metal to react with said sulphur and then provide the molten metal with the required excessa retained magnesium content of from 0.05 to 0.15%. If the foundry is equipped with spectrographic equipment, the magnesium content of the resulting metal is checked before Said metal is poured into molds. In my method of adding the magnesium, I break down the operation into several steps, so as to prevent the uncertainties of desulphurization from interfering with the step whereby the required narrow range of retained magnesium is attained.

In my method, I treat the molten metal with an excess of magnesium so as to desulphurize the molten metal. By an excess, I mean that I add enough magnesium to the molten metal to provide said metal with a retained magnesium content over 0.01%. In order to make sure that there is an excess of magnesium added my usual approach is to add enough magnesium to yield a retained magnesium content of from 0.05 to 0.50%. Thus, for example, if I desire to desulphurize a cupola metal containing, say, 0.125% sulphur, with a magnesium-bearing ferro-silicon that experience has shown is from 80 to 9 efficient in its desulphurizing action, I add surficient of said ferro alloy to the molten metal to yield a magnesium addition of 0.400%, said 0.400% being about 0.10% in excess of the commonly-employed one part of magnesium to one part of sulphur ratio, in view of the lowest efiiciency figure (80%) for magnesium pick-up. If said ferro alloy contains, say, 20% magnesium, this 0.400% addition would involve the addition of 40 pounds of the term alloy per ton of molten iron, equivalent to 8 pounds of magnesium per ton of molten iron.

With the molten metal desulphurized, I treat said metal with a reagent that is oxidizing towards the retained magnesium content of the desulphurized'molten metal. The object of this treatment is to remove the retained magnesium from the molten metal, so as to produce a dependable base metal out of which nodular iron may be conveniently produced; that is, a sulphur and magnesium-free metal. While I prefer a gaseous oxidizing agent, such as oxygen, nitrogen, carbon dioxide, ferric chloride, etc., solid or liquid oxidizing agents may be employed, such as soda ash, caustic soda, ferric oxide, etc. Molten slags, such as soda ash and caustic soda, must be separated sulting in the production of a clean metal. Soda ash or caustic soda may be employed as molten oxidizing slags, or in any convenient mannerthe oxidizing slag to be separated from the molten iron after the oxidation of the magnesium is essentially complete. With soda ash and caustic soda, the two steps in my desulphtu'izing and magnesium oxidation procedure may be carried out by providing the molten sulphur-bearing iron with a cover consisting of molten caustic soda or soda ash, and then introducing the magnesium required for desulphurization into the molten iron so that said magnesium is reacted with said molten iron before said magnesium rises to contact said molten slag-preferably, by introducing the magnesium into the molten iron by leading said magnesium, as a gas, to the bottom of the molten iron bath by means of a refractory tube. And then, after the introduction of magnesium has been continued until the metal is essentially desulphurized and the resulting metal contains a retained magnesium content of at least 0.01%, allowing the magnesium-bearing molten iron to stand in contact with the soda ash or caustic soda until the magnesium content of the metal is eliminated.

Using my sulphur and magnesium free molten iron, the conversion to nodular iron may be ac complished by any conventional method of adding the required magnesium and inoculating agent.

Having now described several forms of my invention, I wish it to be understood that my invention is not to be limited to the specific form or arrangement of steps hereinbefore described, ex cept insofar as such limitations are specified in the appended claims.

I claim as my invention:

1. In the process for producing nodular graphite cast iron by treating molten cast iron containing sulphur with acontrolled amount of magnesium and an inoculating agent, the method of preparing said molten cast iron for conversion into saidnodular graphite cast iron, which comprises: desulphurizing said molten cast iron by reacting said molten cast iron with sufiicient magnesium to produce a molten cast iron containing at least 0.01% retained magnesium; and reacting the resulting desulphurized molten cast iron with a reagent that is oxidizing towards said retained magnesium until the retained magnesium content of said desulphurized molten cast iron has been substantially all oxidized by said reagent.

2. The process according to claim 1 in which said reagent is nitrogen.

3. The process according to said reagent is oxygen.

4. The process according to said reagent is carbon dioxide.

5. The process according to said reagent is ferric chloride.

6. The process according to claim 1 in which said reagent is a molten slag that is oxidizing towards the retained magnesium content of said molten cast iron.

'1' The process according to claim 6 in which said molten cast iron is desulphurized by magnesium as said molten cast iron lies in contact with said molten slag.

JAMES FERNANDO JORDAN.

claim 1 in which claim 1 in which claim 1 in which Name Date. Millie et al. 7 Oct. 25, 1949 Number 

1. IN THE PROCESS FOR PRODUCING NODULAR GRAPHITE CAST IRON BY TREATING MOLTEN CAST IRON CONTAINING SULPHUR WITH A CONTROLLED AMOUNT OF MAGNESIUM AND AN INOCULATING AGENT, THE METHOD OF PREPARING SAID MOLTEN CAST IRON FOR CONVERSION INTO SAID MODULAR GRAPHITE CAST IRON, WHICH COMPRISES: DESULPHURIZING SAID MOLTEN CAST IRON BY REACTING SAID MOLTEN CAST IRON WITH SUFFICIENT MAGNESIUM TO PRODUCE A MOLTEN CAST IRON CONTAINING AT LEAST 0.01% RETAINED MAGNESIUM; AND REACTING THE RESULTING DESULPHURIZED MOLTEN CAST IRON WITH A REAGENT THAT IS OXIDIZING TOWARDS SAID RETAINED MAGNESIUM UNTIL THE RETAINED MAGNESIUM CONTENT OF SAID DESULPHURIZED MOLTEN CAST IRON HAS BEEN SUBSTANTIALLY ALL OXIDIZED BY SAID REAGENT. 